This invention relates to methods for communicating in a control area network, and particularly to such methods in which a listening device in the network listens to a number of devices transmitting data with a common instance.
In controlling various kinds of equipment in homes and buildings, the equipment is often connected to a network through which information is transmitted. Connecting the equipment together in a network system has the advantage that various parts of the system can xe2x80x9ccommunicatexe2x80x9d with each other, whereby the system works with maximum efficiency and potential inconsistencies, such as two parts of the system counteracting each other in operation, can be avoided.
A controller area network may, for example, be used for such purposes. Messages of variable length are transmitted in the network for controlling the system to operate according to provided algorithms. The message frame format includes an identifier at the beginning of each message which provides an identity for each message. The identity may, for example, relate to the kind of data transmitted in a data field of the message.
In a system including several similar devices owning the same identifier, and including at least one listening device which receives the information transmitted by the devices, the system should facilitate that the listening device knows to which devices to listen. It is also important that the network is not overloaded with messages from those devices to which the listening device is not listening. It may be desirable to have several devices connected in a network such that one or more operational modes may be set at any of the devices, whereby the other devices assume the operational mode setting conformly.
One way of arranging a system in accordance with the above would be to configure the information type transmitted by the devices, such that they are all different. This allows every device to transmit its messages regardless of the other devices, since the listening device would be able to distinguish between messagesxe2x80x94and accordingly between data values in the various messagesxe2x80x94from the different devices. However, this method is undesirable in that it requires more initial programming and system configuration than is desirable for the typical home and building control system. Besides the additional work requirement, which may be inconvenient in a home or other building environment, the costs of installation will likely increase with such a solution.
Furthermore, the amount of information transmitted in the network may typically increase with such a method, perhaps causing undesirable jams in data transfer and/or making the system harder to manage. An additional disadvantage is that devices cannot be added, and/or removed from the system without particular reconfiguration and/or readdressing of the existing devices.
A method of communicating between a plurality of devices in an environmental control network includes authorizing a first device to transmit messages with a first identifier over the network, transmitting a first message with the first identifier and a first value from the first device for receipt by at least one second device. The second device, which receives the first message, assumes the first value as its value, and the first and second devices monitor their respective values for changes and transmit their respective values if there are changes. The first device is deauthorized from transmitting messages with the first identifier if it receives a message with the first identifier.
An embodiment of the method according to the invention involves a number of devices and a listening device in a system. At startup of the system, any device which saved its value in a non-volatile memory and has not yet received a value from another device, will become the master of the identifier and transmit a message with the value over the network. Devices which did not save their values in non-volatile memories will transmit requests for the data value. If they do not receive any response, they will become the master and transmit messages with their data. Devices which receive the message will assume the value as theirs. If the value of any device is changed, that device will become master and transmit its changed value over the network.
These and various advantages and features of novelty which characterize the invention are pointed out with particularity in the claims annexed hereto and forming a part hereof. However, for a better understanding of the invention, its advantages, and the objects obtained by its use, reference should be used to the accompanying drawings and descriptive matter which form a further part hereof, and in which there is illustrated and described preferred embodiments of the invention.